The fabrication of an integrated circuit chip typically begins with a thin, polished slice of high-purity, single-crystal semiconductor material substrate (such as silicon or germanium) called a “wafer.” Each wafer is subjected to a sequence of physical and chemical processing steps that form the various circuit structures on the wafer. During the fabrication process, various types of thin films may be deposited on the wafer using various techniques such as thermal oxidation to produce silicon dioxide films, chemical vapor deposition to produce silicon, silicon dioxide, and silicon nitride films, and sputtering or other techniques to produce other metal films.
After depositing a film on the semiconductor wafer, the unique electrical properties of semiconductors are produced by substituting selected impurities into the semiconductor crystal lattice using a process called doping. The doped silicon wafer may then be uniformly coated with a thin layer of photosensitive, or radiation sensitive material, called a “resist.” Small geometric patterns defining the electron paths in the circuit may then be transferred onto the resist using a process known as lithography. During the lithographic process, the integrated circuit pattern may be drawn on a glass plate called a “mask” and then optically reduced, projected, and transferred onto the photosensitive coating.
The lithographed resist pattern is then transferred onto the underlying crystalline surface of the semiconductor material through a process known as etching. Vacuum processing chambers are generally used for etching and chemical vapor deposition (CVD) of materials on substrates by supplying an etching or deposition gas to the vacuum chamber and application of a radio frequency (RF) field to the gas to energize the gas into a plasma state.
A reactive ion etching system typically consists of an etching chamber with an upper electrode or anode and a lower electrode or cathode positioned therein. The cathode is negatively biased with respect to the anode and the container walls. The wafer to be etched is covered by a suitable mask and placed directly on the cathode. A chemically reactive gas such as CF4, CHF3, CClF3, HBr, Cl2 and SF6 or mixtures thereof with O2, N2, He or Ar is introduced into the etching chamber and maintained at a pressure which is typically in the millitorr range. The upper electrode is a showerhead electrode provided with gas outlet(s), which permit the gas to be uniformly dispersed through the electrode into the chamber. The electric field established between the anode and the cathode will dissociate the reactive gas forming plasma. The surface of the wafer is etched by chemical interaction with the active ions and by momentum transfer of the ions striking the surface of the wafer. The electric field created by the electrodes will attract the ions to the cathode, causing the ions to strike the surface in a predominantly vertical direction so that the process produces well-defined vertically etched sidewalls.
Reliable and repeatable temperature control of the showerhead electrode during plasma processing of semiconductor substrates is desirable for achieving desired plasma chemistry at the plasma exposed surface of the showerhead electrode. Commonly owned U.S. Published Patent Application Nos. 2009/0081878 and 2008/0308228, the disclosures of which are hereby incorporated by reference, disclose temperature control modules for showerhead electrode assemblies.
Servicing of showerhead electrodes can be difficult due to complicated mounting arrangements. Commonly assigned U.S. Non-Provisional patent application Ser. No. 12/216,524 filed on Jul. 7, 2008 discloses a monolithic showerhead electrode which is removably attached to a backing plate by a series of cam locks. In the embodiment shown, the backing plate has an annular projection housing the cam locks and the showerhead electrode has an annular recess which mates with the projection on the backing plate.
In some plasma processes, it would be desirable to provide a gas outlet pattern which distributes process gas more uniformly in the chamber.
Disclosed herein is a clamped monolithic showerhead electrode having improved gas distribution and temperature control.